Conventional twin-clutch apparatuses have a hydraulic first disk clutch and a hydraulic second disk clutch arranged coaxially, the clutches exerting a predetermined engaging force by pressure members displaced by the pressure of an oil supplied from the outside. The twin-clutch apparatuses are used for reducing slippage while driving in a semi-automatic transmission mode and for reducing a transmission shock at the time of start through appropriately switching between the first disk clutch and the second disk clutch.
Here, the first disk clutch and the second disk clutch play a different role. Therefore, they may have a different requirement in clutch capacity. For example, in Patent Document 1, a first clutch plate and a second clutch plate have a difference in diameter, to thereby bring about a difference in clutch capacity.    Patent Document 1: Japanese Unexamined Patent Publication, First Publication